fix: set prometheus authentication variable

src/charm.py

@@ -100,6 +100,9 @@ def main(self, event):
                         # than an environment variable, but we cannot use that using podspec.
                         # (see https://stackoverflow.com/questions/37317003/restart-pods-when-configmap-updates-in-kubernetes/51421527#51421527)  # noqa E403
                         "configmap-hash": configmap_hash,
+                        # To allow public access without authentication for prometheus
+                        # metrics set environment as follows.
+                        "MINIO_PROMETHEUS_AUTH_TYPE": "public",
                     },
                     "volumeConfig": [
                         {

tests/integration/test_charm.py

@@ -269,6 +269,12 @@ async def test_prometheus_grafana_integration(ops_test: OpsTest):
             assert response_metric["juju_application"] == APP_NAME
             assert response_metric["juju_model"] == ops_test.model_name
 
+            # Assert the unit is available by checking the query result
+            # The data is presented as a list [1707357912.349, '1'], where the
+            # first value is a timestamp and the second value is the state of the unit
+            # 1 means available, 0 means unavailable
+            assert response["data"]["result"][0]["value"][1] == "1"
+
 
 # Helper to retry calling a function over 30 seconds or 5 attempts
 retry_for_5_attempts = Retrying(